This invention relates to a laser COM device in which the relative positions of character images formed by an intensity modulated laser scan and a separately projected format slide image superimposed on the character images on a recording medium can be electrically adjusted with high precision and resolution.
The term COM is an abbreviation for a Computer Output Microfilmer in which computer output data is optically superimposed on a format slide image having ruled lines or the like and recorded on a microfilm. In early COM devices the output data was displayed in the form of numerals or characters on a cathode ray tube, and an optical image thereof was formed on a silver salt film by a lens system. More recently, highly stable and low cost laser COM devices have been developed in which a laser instead of a cathode ray tube is employed as the light source. The laser beam is intensity modulated and deflected in two dimensions to scan a microfilm, thereby implementing recording. As compared with a cathode ray tube COM, the laser COM provides considerably higher brightness and energy output, whereby inexpensive recording materials having a relatively low sensitivity may be used. For example, Dry Silver and diazo films can be used, as well as a heat mode recording material such as thin metal film. The use of such recording materials also eliminates the troublesome wet development process.
As a COM device records very small images on a high density recording material, extremely high deflection accuracy is required. If the recorded image lies on the ruled lines of a format slide, reading is very difficult even if the image is greatly enlarged. The relative positions of the recorded image and the ruled lines must therefore be correctable so that they do not overlie one another.
In one method of deflecting the laser beam in a COM a device using electro-optical or acousto-optical effects is employed, which provides a very fast or high velocity deflection. This method is characterized by poor resolution and reduced brightness, however. A mechanical deflection device such as a rotary multi-surfaced mirror or a vibrating mirror is therefore commonly employed, but with such means the adjustment of the relative positions of the data image and the ruled line image is very difficult. Such relative position deviations may be corrected by finely moving the frame or base holder of the format slide using a micrometer, but the provision of such means is very expensive due to the degree of precision required. In addition, the image is liable to be affected by vibrations or the like during such fine adjustment.